This invention relates to automatic drain valves for automatically draining condensate liquid from accumulator or receiver tanks, piping, hoses and other components of compressor systems.
Compressed air is widely used for industrial purposes such as removing debris from manufactured parts or equipment and for energizing a wide variety of industrial devices and equipment. When air is compressed by a compressor, water is often produced as a condensate. This water, frequently mixed with oil and other contaminants, accumulates in the lowest point of a compressed air receiver or in the piping, hoses or other components of a compressor system. If this water is not periodically removed from the compressor system, it accumulates to the point where it can dramatically reduce the volume capacity of the receiver. The accumulated water also promotes rust and corrosion of the compressor system's components, as well as the devices and equipment which are energized by compressed air.
To allow the removal of condensate from a compressor system, a drain valve is often installed at a low point of the receiver tank. Compressor systems which have a large network of distribution piping may also have drain valves installed at low points in the piping to allow condensate to be removed.
Over the years many different types of drain valves have been developed and used in compressor systems. Each type of drain valve has its own strengths and weaknesses with respect to the removal of liquid condensate. By way of example, manual drain valves are operated by hand to remove the accumulating liquid condensate until an operator determines all the liquid has been removed. The weakness of these valves is that if their regular operation is neglected, the condensate continues to accumulate, the volume capacity of the receiver is reduced and rust and corrosion are more likely to occur in the compressor system and in devices and equipment operated by compressed air from the system.
Other drain valves operate automatically through the use of a timer. A weakness of this type of drain valve is that cycle times are sometimes set so that they operate too infrequently to keep up with the varying amounts of liquid condensate, thereby allowing it to accumulate. Or the cycle times may be too frequent, resulting in the drain valve staying open after liquid is removed. As a result, large quantities of pressurized air are allowed to escape on each timed cycle of the valve.
Other automatic drain valves open and close with the presence or absence of liquid in the receiver or in other parts of the compressed air system which are being monitored. The advantage of this type of drain valve is that it opens only on the accumulation of a preselected amount of liquid and closes before a significant amount of pressure can escape. The disadvantage of this type of drain valve is that it normally depends on floats and other mechanical mechanisms. These mechanisms may not drain all the accumulated liquid, leaving a fixed amount of condensate permanently in a receiver, for example, to cause rust or corrosion damage. This type of drain valve is also known to be susceptible to failure due to friction caused by the fouling of valve pistons and seats and the failure of floats and other mechanisms. Additionally, this type of drain valve requires careful selection of a combination of floats and orifices to achieve proper operation.
Still other drain valves operate when electrical sensors detect the presence of a preselected amount of accumulated liquid. This type of drain valve tends to be more complex, expensive and difficult to maintain in comparison with mechanical drain valves. Drain valves operating in response to electrical liquid accumulation sensors are also relatively sensitive to the failure of mechanical parts and are known to be inherently susceptible to more frequent failure due to the fouling of liquid sensors with contaminants. Additionally, this type of drain valve generally does not drain all of the liquid which is available to be drained, leaving an amount of condensate permanently within the system.
Compressed air receivers undergo cyclic changes in the pressure of the air within them as air is used and is then replaced by operation of a compressor. Still other drain valves operate based on these known pressure cycles. Such drain valves generally open the drain for a fixed period of time, once or twice during each pressure cycle. Since they open the drain for approximately the same time whether or not liquid is present, they potentially waste large volumes of compressed air when little or no liquid is present in the receiver. Alternatively, when a large amount of liquid is present, these drain valves tend to become overwhelmed and are unable to drain the increasing amount of condensate present within the system, thereby gradually increasing the level of condensate in the receiver and other components of the system.
A drain valve which is the subject of U.S. Pat. No. 4,222,403 Sonora includes a pair of pistons, one having a valve surface which controls liquid flow through an inlet port and the other having a valve surface which controls liquid flow through an outlet port. Both pistons are actuated to open both the inlet port and the outlet port to drain liquid from a compressor at the point where the compressor is unloaded during each of its operating cycles. That is, this valve operates when the desired maximum pressure of the system is reached and the compressor is no longer increasing the pressure in the system. This drain valve is then closed by expanding compressed air at the end of the flow of liquid, avoiding a substantial loss of compressed air. However, this drain valve requires a separate, three-way valve, such as a solenoid valve, to operate it when the maximum pressure of the system is reached, adding an extra component to a compressed air system which is not normally present. It also uses several sliding O-rings on the two pistons. These O-rings are susceptible to damage due to frictional forces. As a result, this drain valve can be expected to require increased maintenance in comparison to valves which do not use sliding O-rings.